The use of urea aldehyde resins containing lignin sulfonate is well know in the Art but the use of amino compounds such as urea, guanidine, cyanoguanidine, aminoguanidine, guanidine carbonates and mixtures thereof for delignification of lignin from biomass consisting of lignin containing plants and at the same time reacting the amino compound with lignin and with lignin still attached to the cellulose is novel before reacting the amino compound with a plant protein and/or carbohydrate. There are many US and Foreign Patents which utilized urea formaldehyde resin containing lignin sulfonate and other extracted lignin but no articles or patents were found that produces amino lignin in the process of delignification of biomass containing lignin. U.S. Pat. No. 2,366,265 of Reiche et al. and U.S. Pat. No. 2,622,979 of Keim extends the urea formaldehyde resin by the addition of lignin-sulfonate. U.S. Pat. No. 3,994,860 of Willegger and Thiel adds the lignin sulfonate to the formaldehyde and urea to produce a resin. The use of aminoplasts as an adhesive and resin is well known in the art but an aqueous solution of the aminoplasts such as urea formaldehyde resin does not have any properties to break the lignin cellulose bond. Unlike the prior art processes of these representative patents, in accordance with this invention most of the lignin and cellulose bonds are broken by the amino compound and the amino reacts with the lignin to produce an amino lignin and amino lignin cellulose and releases the hemi-cellulose.
The adhesive composition may also include additives and fillers found in lignocellulosic adhesives such as bactericide, insecticides, silica, wheat flour, tree bark flour, lignin cellulose, nut shell flour and the like.
The adhesive compositions are heat-curable but may be cured at ambient temperature and pressure. Curing typically occurs during the hot pressing step of the lignocellulosic composite formation. Thus, the cure temperature of the adhesive composition is tailored so that it coincides with the heating temperatures used in composite formation. Such cure temperatures may range, for example, from about 100 to about 200 degree. C., more particularly from about 120 to about 225.degree C.
The adhesive components will react together when in a non-aqueous solution by mixing the amino compound, biomass containing lignin in a moist condition and plant protein and/or carbohydrate when under heat and pressure to produce hard and strong lignocellulosic composites
Lignocellulosic composites that can be produced with the adhesives described herein include particleboard, oriented strand board (OSB), wafer board, fiberboard (including medium-density and high-density fiberboard), parallel strand lumber (PSL), laminated strand lumber (LSL), and similar products. In general, these composites are made by first blending comminuted lignocellulosic materials with an adhesive that serves as a binder that adheres the comminuted lignocellulosic materials into a unitary densified mass. Examples of suitable lignocellulosic materials include wood, straw (including rice, wheat and barley), flax, hemp and bagasse. The comminuted lignocellulosic materials can be in any processed form such as chips, flakes, fibers, strands, wafers, trim, shavings, sawdust, straw, stalks and shivs. The resultant mixture is formed into the desired configuration such as a mat, and then processed, usually under pressure and with heat, into the final product. Processes are generally carried out at temperatures of from about 120 to 225 degree C. in the presence of varying amounts of steam, generated by liberation of entrained moisture from the lignocellulosic materials. Thus, the moisture content of the lignocellulose material may be between about 2 and about 20 percent by weight, before it is blended with the adhesive.
The amount of adhesive mixed with the lignocellulosic particles may vary depending, for example, upon the desired composite type, lignocellulosic material type and amount of, and particular type of, adhesive composition. In general, about 1 to about 12, more particularly about 3 to about 10, weight percent adhesive may be mixed with the lignocellulosic material, based on the total combined weight of adhesive and lignocellulosic material. The mixed adhesive composition may be added to the comminuted lignocellulosic particles by spraying or similar techniques while the lignocellulosic particles are tumbled or agitated in a blender or similar mixer. For example, a stream of the comminuted lignocellulosic particles may be intermixed with a stream of the mixed adhesive composition and then be subjected to mechanical agitation.
The adhesive compositions also may be used to produce plywood, hardboard or laminated veneer lumber (LVL). The adhesive composition may be applied onto veneer surfaces by roll coating, knife coating, curtain coating, or spraying. A plurality of veneers are then laid-up to form sheets of required thickness. The mats or sheets are then placed in a heated press (e.g., a platen) and compressed to effect consolidation and curing of the materials into a board. Fiberboard may be made by the wet felted/wet pressed method, the dry felted/dry pressed method, or the wet felted/dry pressed method.
The presently disclosed adhesive provides a strong bond between the lignocellulosic particles or fractions. The adhesive also provides structural composites with high mechanical strength. In addition, the adhesive composition is substantially free of formaldehyde (including any compounds that may degenerate to form formaldehyde). For example, the adhesive compositions do not contain any formaldehyde (and formaldehyde-generating compounds) that is detectable by conventional methods or, alternatively, the amount of formaldehyde (and formaldehyde-generating compounds) is negligible from an environmental and workplace regulatory standpoint.